The invention relates to a pneumatic gripper for bobbin changer devices provided on spinning machines or twisting machines. The pneumatic gripper includes a gripper housing and an elastically deformable collar arranged therein and adapted to be pressed against the outer circumference of a bobbin sleeve by pressurized air.
A pneumatic gripper with an elastically deformable collar, which is pressed against the outer circumference of a bobbin sleeve when pressurized air is fed into the gripper, is known (German Pat. No. 1,180,285). This gripper, intended for doffer devices in continuously operating bobbin changers for spinning machines, has a gripping head which is attached by means of a flexible hose to a pressurized air source and is mounted with free mobility in its support in order to compensate movement fluctuations. A sleeve, which is fixed to the lower part of the gripper head, serves to receive an annular rubber collar of U-shaped cross-section. Pressurized air can be introduced into and released from the annular collar, the outer edge and inner edge of which are pressed airtightly against the gripper head, through a longitudinal bore in the gripper head. When pressurized air is introduced, the inner part of the annular collar is pressed against the free end of the bobbin sleeve projecting beyond the sleeve winding, so that this sleeve is retained in the gripping orifice of the gripper and the bobbin can be doffed from the spindle by raising the gripper. When the gripper releases the bobbin, a striker which projects into the gripping orifice and is required for the centering of the gripper head in its support, acts as an ejector.
The disadvantages of the known gripper are the technical production outlay and the movement of the annular collar relative to the wall of the sleeve surrounding it which occurs when pressurized air is fed into the gripper. The annular collar is subjected to wear as a result of this relative movement. Since the gripper engages only the free end of the bobbin sleeve projecting beyond the winding, a high pressure is also required to generate a sufficiently intense clamping of the bobbin sleeve. Furthermore, the directional stability in the holding of the bobbin sleeve is impaired by the fact that the folds which form on the inner part of the annular collar when the gripper is inflated are braced against the moving outer part of the annular collar. The known pneumatic gripper is, therefore, less suitable for the creeling of bobbin sleeves on spindles or journals which demands high directional stability.